But the fruit of their labours — fuel made from just sunlight, water and carbon dioxide — could prove endless.

"This technology means we might one day produce cleaner and plentiful fuel for planes, cars and other forms of transport," noted Máire Geoghegan-Quinn, European commissioner for research, innovation and science, in a press release. "This could greatly increase energy security and turn one of the main greenhouse gases responsible for global warming into a useful resource."

To produce the fuel, researchers moved water and carbon dioxide through a solar reactor at 700°C. At that temperature, they separate and form a synthetic gas, composed of hydrogen and carbon monoxide.

"The basic idea is to reverse the combustion process," Germany-based project leader Patrick Le Clercq told the Daily Mail. "What we do is take carbon dioxide and water vapour, and introduce energy to produce fuel."

A process, dubbed Fischer-Tropsch, is then used to to transform the compressed gas into a fuel that burns similarly to kerosene.

"Increasing environmental and supply security issues are leading the aviation sector to seek alternative fuels which can be used interchangeably with today’s jet fuel," project coordinator Andreas Sizmann noted in the press release.

"With this first-ever proof-of-concept for 'solar' kerosene, the SOLAR-JET project has made a major step towards truly sustainable fuels with virtually unlimited feedstocks in the future.’

The future, however, will sip of more than a mere jar-full of the stuff.

To that end, scientists say they can build a full-scale solar concentrator that could generate some 20,000 litres of jet fuel a day.

"This is an extremely important milestone in the long-term process of developing a truly sustainable alternative fuel future," he says. "The process [draws] from virtually unlimited resources with no prohibitive cost 'show stopper' in sight."

European chemists aren't the only researchers edging closer to a renewable energy source.

"Many groups around the world are working on the same process using different reactors, but [have] the same goal of reaching commercially viable solar-to-fuel efficiency,’ engineer Jane Davidson at the University of Minnesota told Chemistry World.

"It’s an exciting approach to synthetic fuels that also stores solar energy in chemical form."